JP5508038B2 - Studless tires for trucks / buses or light trucks - Google Patents

Description

The present invention relates to a studless tire for a truck / bus or a light truck.

In order to prevent dust pollution caused by spiked tires, the prohibition of the use of spiked tires was legalized, and studless tires were used instead of spiked tires in cold regions. In order to improve the grip performance of the studless tire on ice or snow, there is a method of improving the adhesive friction by reducing the elastic modulus at low temperature. In particular, the braking force on ice is greatly affected by the effective contact area between rubber and ice, and therefore, a flexible rubber at low temperature is required to increase the effective contact area.

On the other hand, if only the hardness of the rubber is lowered by a method such as increasing the amount of oil, in the studless tire for trucks, buses, or light trucks, uneven wear resistance and steering stability of the tread portion are lowered.

Furthermore, in recent years, due to the effects of global warming or the fact that the replacement of summer tires is troublesome, the tires are often run on studless tires other than icy and snowy roads. Sex is increasingly required. Especially for truck / bus or light truck studless tires, the wear resistance of the tread is an especially important characteristic. As mentioned above, the oil amount can be increased by simply increasing the amount of oil. When attempting to increase the braking performance, there arises a problem that the wear resistance decreases.

In general, a tread rubber of a studless tire is often made mainly of natural rubber or butadiene rubber because of its high strength but low glass transition temperature and flexibility (see, for example, Patent Document 1). However, natural rubber and butadiene rubber produce reversion (reversion) when sulfur vulcanized. This phenomenon is that the rubber deteriorates and the cross-linked state deteriorates. At this time, the elastic modulus at low temperature also decreases, but the hardness also decreases more than necessary, and the steering stability and wear resistance decrease. As a result of the present inventors' research, it has been found out. In addition, when vulcanization reversion occurs, tan δ at a high temperature is unnecessarily increased, and fuel efficiency, which is a very important characteristic, is reduced in a truck / bus / light truck.

Not only studless tires but also vulcanization may be performed at higher temperatures in order to increase the productivity of the tires. In such a case, the above phenomenon becomes particularly prominent. In addition, there is a problem that wear resistance and fuel consumption are further reduced by reversion.

In addition, as a method for suppressing the reversion of vulcanizable rubber compositions used in rubber products such as tires and improving the heat resistance, the amount of vulcanization accelerator with respect to sulfur as a vulcanizing agent is conventionally used. There are known methods for increasing the amount of sulfur and methods for blending thiuram vulcanization accelerators as vulcanization accelerators. Further, as a crosslinking agent capable of forming a long-chain crosslinked structure represented by — (CH ₂ ) ₆ —S— or the like, PERIKALIN 900 manufactured by Flexis, Duralink HTS, Vulcuren KA9188 manufactured by Bayer, and the like are known. It is known that the reversion of the rubber composition can be suppressed by blending these crosslinking agents into the rubber composition. However, when these methods are used, reversion can be suppressed, but there is a problem that the fuel economy and wear resistance are lowered and the performance balance is deteriorated. Furthermore, these techniques are effective in suppressing reversion of natural rubber and isoprene rubber, but there is also a problem that butadiene rubber has no effect or little effect.

As another method for suppressing vulcanization reversion, Patent Document 2 describes that vulcanization reversion is suppressed by blending a natural rubber with a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid. It is disclosed that it can be done. However, application to butadiene rubber has not been studied in detail.

JP 2007-169500 A JP 2007-321041 A

The present invention solves the above-described problems and achieves a high-performance truck that achieves both good braking force on ice and snow, uneven wear resistance, handling stability, and even good rolling resistance characteristics and wear resistance.・ To provide studless tires for buses or light trucks. It is another object of the present invention to produce the studless tire with higher production efficiency and provide it to consumers at a lower cost.

As a result of intensive studies, the present inventors have found that a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid is particularly effective for vulcanization reversion of butadiene rubber, and is a composition containing silica. It was also found that the processability of the composition can be improved and the reversion of the composition containing silica can be more effectively suppressed. Furthermore, as a result of investigation, a rubber composition containing a butadiene rubber and a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid has a problem in the tire molding process due to a decrease in rubber surface tackiness. It has been newly found that there is a possibility of the occurrence of. Therefore, as a result of diligent investigations on the newly generated problems, the above problem is achieved by making the rubber composition substantially free of stearic acid that is usually blended in a rubber composition for tires as a vulcanization aid. And found that new problems can be solved at the same time.
That is, the present invention includes a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, containing 35% by mass or more of butadiene rubber in 100% by mass of the rubber component, and substantially containing stearic acid. The present invention relates to a truck / bus or light truck studless tire using a rubber composition containing no rubber as a tread.

It is preferable that the rubber composition further contains 5 parts by mass or more of silica with respect to 100 parts by mass of the rubber component.

According to the present invention, it contains a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, contains 35% by mass or more of butadiene rubber in 100% by mass of the rubber component, and substantially contains stearic acid. By using a rubber composition that does not contain in the tread, good braking force on ice and snow, uneven wear resistance, handling stability, and also good rolling resistance characteristics, wear resistance, and tackiness (tire molding) It is possible to provide a high-performance truck / bus or light truck studless tire that is compatible with the workability at the time. In addition, about the improvement of adhesiveness, since the component which precipitates on the rubber surface decreased by not containing stearic acid substantially, it is estimated that adhesiveness improved.

The studless tire for trucks / buses or light trucks of the present invention contains a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, and 35% by mass or more of butadiene rubber in 100% by mass of the rubber component. A rubber composition containing tear and containing substantially no stearic acid is used.

The rubber composition contains 35% by mass or more of butadiene rubber in 100% by mass of the rubber component. The lower limit of the butadiene rubber content is preferably 40% by mass, more preferably 45% by mass, and most preferably 55% by mass. The upper limit is preferably 80% by mass, more preferably 70% by mass, and most preferably 65% by mass. If it is less than 35% by mass, it will be difficult to lower the glass transition temperature, and the braking force on ice and snow will be reduced. If it exceeds 80% by mass, the performance on ice and snow will be good, but the mechanical strength and abrasion resistance will be improved. Tend to decrease. In the present invention, the ratio of the butadiene rubber can be increased to achieve both wear resistance and performance on ice and snow.

As the butadiene rubber, a butadiene rubber having a cis content of 95% by mass or more and a 5% toluene solution viscosity at 25 ° C. of 80 cps or more may be blended. By blending such butadiene rubber, the effect of improving wear resistance is improved. The toluene solution viscosity is preferably 200 cps or less. If it exceeds 200 cps, the viscosity tends to be too high, and the processability tends to be reduced, or it tends to be difficult to mix with other rubber components. The lower limit of the viscosity is preferably 110 cps, and the upper limit is preferably 150 cps.

When the molecular weight distribution (Mw / Mn) of butadiene rubber is 3.0 or less, the wear resistance can be improved. Furthermore, you may use the butadiene rubber whose Mw / Mn is 3.0-3.4. By using such butadiene rubber, it is possible to achieve both improvement in workability and improvement in wear resistance.

When a mixture of butadiene rubber and other rubber components is used as the rubber component, the other rubber components are not particularly limited. For example, natural rubber (NR), epoxidized natural rubber (ENR), styrene butadiene rubber (SBR) ), Isoprene rubber (IR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (X-IIR) and the like. Among them, it is preferable to include NR and / or ENR because it is environmentally friendly, can be prepared for a future decrease in the amount of oil supply, and can further improve wear resistance.

The rubber component includes at least one functional group selected from the group consisting of an alkoxyl group, an alkoxysilyl group, an epoxy group, a glycidyl group, a carbonyl group, an ester group, a hydroxy group, an amino group, and a silanol group (hereinafter referred to as a functional group). May be included. As the rubber having these functional groups, commercially available rubbers may be used, or they may be appropriately modified and used.

When butadiene rubber is used by mixing with natural rubber or polyisoprene rubber, the rubber component preferably contains a total amount of these rubber components of 70% by mass or more. By setting it to 70% by mass or more, good performance on ice and snow and wear resistance can be achieved, and the effect of reversion resistance can be increased. The blending amount of these rubber components is more preferably 80% by mass or more, further preferably 90% by mass or more, and most preferably 100% by mass.

The rubber composition contains a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid. The mixture is particularly effective in reversion of butadiene rubber, and can improve the processability of a composition containing silica, and more effectively suppress reversion of the composition containing silica. be able to.

Aliphatic carboxylic acids include palm oil, palm kernel oil, camellia oil, olive oil, almond oil, canola oil, peanut oil, rice sugar oil, cocoa butter, palm oil, soybean oil, cottonseed oil, sesame oil, linseed oil, castor oil Examples include aliphatic carboxylic acids derived from vegetable oils such as rapeseed oil, aliphatic carboxylic acids derived from animal oils such as beef tallow, and aliphatic carboxylic acids chemically synthesized from petroleum, etc. It is also possible to prepare for a decrease in the supply amount of the oil, and further, since the vulcanization reversion can be sufficiently suppressed, an aliphatic carboxylic acid derived from vegetable oil is preferable, and an aliphatic carboxylic acid derived from palm oil, palm kernel oil or palm oil is preferred. More preferred.

The aliphatic carboxylic acid preferably has 4 or more carbon atoms, more preferably 6 or more carbon atoms. If the aliphatic carboxylic acid has less than 4 carbon atoms, the dispersibility tends to deteriorate. The aliphatic carboxylic acid preferably has 16 or less carbon atoms, more preferably 14 or less, and even more preferably 12 or less. When the number of carbon atoms of the aliphatic carboxylic acid exceeds 16, there is a tendency that reversion can not be sufficiently suppressed.

The aliphatic group in the aliphatic carboxylic acid may be a chain structure such as an alkyl group (straight chain structure or branched structure) or a cyclic structure such as a cycloalkyl group.

In addition, some zinc salts of aliphatic carboxylic acids are liquid at room temperature, but when they are liquid, handling may be difficult. However, even in such a case, handling is facilitated by using a material supported on silica or the like.

Examples of the aromatic carboxylic acid include benzoic acid, phthalic acid, mellitic acid, hemimellitic acid, trimellitic acid, diphenic acid, toluic acid, and naphthoic acid. Of these, benzoic acid, phthalic acid, or naphthoic acid is preferable because reversion can be sufficiently suppressed.

Content ratio of zinc salt of aliphatic carboxylic acid and zinc salt of aromatic carboxylic acid in the mixture (molar ratio: zinc salt of aliphatic carboxylic acid / zinc salt of aromatic carboxylic acid, hereinafter referred to as content ratio) is 1/20 or more is preferable, 1/15 or more is more preferable, and 1/10 or more is more preferable. If the content ratio is less than 1/20, it is not possible to consider the environment or prepare for a future reduction in the amount of petroleum supply, and the dispersibility and stability of the mixture tend to deteriorate. Further, the content ratio is preferably 20/1 or less, more preferably 15/1 or less, and further preferably 10/1 or less. When the content ratio exceeds 20/1, there is a tendency that the vulcanization return cannot be sufficiently suppressed.

The zinc content in the mixture is preferably 3% by mass or more, and more preferably 5% by mass or more. If the zinc content in the mixture is less than 3% by mass, there is a tendency that the vulcanization return cannot be sufficiently suppressed. Moreover, 30 mass% or less is preferable and, as for the zinc content rate in a mixture, 25 mass% or less is more preferable. When the zinc content in the mixture exceeds 30% by mass, the workability tends to decrease and the cost increases unnecessarily.

The content of the mixture is 0.2 parts by mass or more, preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and most preferably 1.4 parts by mass or more with respect to 100 parts by mass of the rubber component. When the content of the mixture is less than 0.2 parts by mass, the effect of suppressing reversion is not sufficient, and it is difficult to obtain a sufficient improvement effect. The content of the mixture is 10 parts by mass or less, preferably 7 parts by mass or less, more preferably 5 parts by mass or less. When the content of the mixture exceeds 10 parts by mass, the tendency to bloom increases, and the improvement of the effect with respect to the added amount decreases, and the cost increases unnecessarily.

The rubber composition of the present invention is substantially free of stearic acid.
The content of stearic acid is preferably 0.05 parts by mass or less, more preferably 0.01 parts by mass or less, still more preferably 0.001 parts by mass or less, and most preferably 0 parts by mass with respect to 100 parts by mass of the rubber component. Part (does not contain).
Stearic acid is usually blended in a tire rubber composition as a vulcanization aid. In the case where stearic acid is not blended, it is expected that problems such as a long vulcanization time and a large disadvantage in terms of the process will occur. However, in the present invention, a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid serves as a vulcanization aid, and further reduces bloom, so that the above problem does not occur. It is.

When oil or a plasticizer is contained, the blending amount thereof is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 2 parts by mass or less, based on 100 parts by mass of the rubber component. Mass parts (not contained) are most preferred. When these components are contained in a large amount, the wear resistance is lowered, and the reversion resistance is sometimes lowered. Even with aroma oil or alternative aroma oil with relatively low wear resistance, the low-temperature characteristics may deteriorate and the performance on ice and snow may deteriorate, or the tan δ at high temperatures may increase and the rolling resistance may deteriorate. is there.

The rubber composition preferably further contains 5 parts by mass or more of silica with respect to 100 parts by mass of the rubber component. By blending silica, it is possible to improve on-ice braking performance and on-ice handling stability which are important as a studless tire. In particular, a mixture of a zinc salt of an aliphatic carboxylic acid and an aromatic carboxylic acid can improve the processability of silica blending and more effectively suppress reversion with silica blending. Further, when silica is blended, the above-described rubber surface adhesiveness is lowered, and the newly generated problem that there is a possibility of causing a problem in the tire molding process can be solved more sufficiently. Examples of the silica include silica produced by a wet method and silica produced by a dry method, but there is no particular limitation.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is 40 m ² / g or more, preferably 50 m ² / g or more. When N ₂ SA of silica is less than 40 m ² / g, the reinforcing effect is insufficient. N ₂ SA of silica is 450 m ² / g or less, preferably 400 m ² / g or less. If the N ₂ SA of silica exceeds 450 m ² / g, the dispersibility decreases, and the heat build-up of the rubber composition increases, which is not preferable.

The content of silica is 5 parts by mass or more, preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and most preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. If the silica content is less than 5 parts by mass, it tends to be difficult to improve the braking performance on ice and the steering stability on ice. The silica content is 150 parts by mass or less, preferably 120 parts by mass or less, and more preferably 100 parts by mass or less. When the content of silica exceeds 150 parts by mass, workability and workability deteriorate, which is not preferable.

As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-tri Ethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilyl) Butyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) Trisulf Bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis ( 4-triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N , N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxy Rylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxy Sulfide series such as silylpropyl methacrylate monosulfide, mercapto series such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, vinyltriethoxysilane , Vinyl type such as vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3- (2-amino Noethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, and other amino compounds, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycid Glycidoxy type such as xylpropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, nitro type such as 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3 -Chloro series such as chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-chloroethyltriethoxysilane, and the like. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent is 1 part by mass or more, preferably 2 parts by mass or more with respect to 100 parts by mass of silica. If content of a silane coupling agent is less than 1 mass part, the effect by containing a silane coupling agent is not enough. Moreover, content of a silane coupling agent is 20 mass parts or less with respect to 100 mass parts of silica similarly, Preferably it is 15 mass parts or less. When the content of the silane coupling agent exceeds 20 parts by mass, a coupling effect cannot be obtained for an increase in cost, and the reinforcing property and wear resistance are deteriorated.

In addition to the rubber component, a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, silica, and a silane coupling agent, the rubber composition of the present invention includes a compounding agent conventionally used in the rubber industry. For example, fillers such as carbon black and eggshell powder, softeners, antioxidants, antiozonants, antioxidants, vulcanization accelerators, zinc oxides, vulcanizing agents such as peroxides and sulfur, A sulfur accelerator may be contained.

As carbon black, carbon black having an average particle size of 22 nm or less and / or a DBP oil absorption of 115 ml / 100 g or more is preferable. By blending such carbon black, it provides the tread with the necessary reinforcement for truck / bus or light truck studless tires, ensuring block rigidity, steering stability, uneven wear resistance, and wear resistance. be able to. In addition, the rubber composition containing carbon black tends to be deteriorated in processability, but the rubber composition used in the present invention contains a mixture of a zinc salt of an aliphatic carboxylic acid and an aromatic carboxylic acid. Can reduce the viscosity of the unvulcanized rubber and improve the processability.

The content of carbon black is 15 parts by mass or more, preferably 25 parts by mass or more, more preferably 35 parts by mass or more, and most preferably 40 parts by mass or more with respect to 100 parts by mass of the rubber component. If the carbon black content is less than 15 parts by mass, the reinforcing property is insufficient, and it tends to be difficult to ensure the required block rigidity, steering stability, uneven wear resistance, and wear resistance. The carbon black content is 120 parts by mass or less, preferably 80 parts by mass or less, and more preferably 60 parts by mass or less. When the content of carbon black exceeds 120 parts by mass, processability deteriorates and hardness becomes too high.

The eggshell powder is blended with the rubber component so that (A) the chicken eggshell powder itself scratches the snowy snow road surface, and (B) the pores present in the chicken eggshell powder particles absorb the water on the snowy snow road surface. (C) The effect that the pores formed by dropping the eggshell powder particles absorb the water on the ice and snow road surface, and (D) The pores formed by dropping the eggshell powder particles The effect of (A) to (D), ie, the effect of scratching the snowy and snowy road surface, is obtained. Thus, the improvement in performance on ice is largely attributed to the scratching effect and the water removal effect by the pores present in the eggshell powder particles or the pores obtained by dropping off the eggshell powder particles. .

The eggshell powder consists of (1) chicken egg shell powder having an average particle diameter of 20 μm or less and (2) chicken egg shell powder having an average particle diameter of 40 to 200 μm.

Adding a small particle size such as eggshell powder (1) produces more irregularities on the surface of the rubber composition than when mixing the same amount of larger particle size, improving the scratching effect The effect of making it get.

Moreover, when a thing with a large particle diameter like eggshell powder (2) is mix | blended, the effect that the surface roughness of a rubber composition surface will be enlarged and the scratching effect will be improved is acquired.

By combining eggshell powder (1) and (2), large and small pores are produced on the tread surface, and small pores produce a lot of wrinkles, resulting in a scratching effect, while large pores produce a water absorption effect. Thus, a synergistic effect of the chicken eggshell powders (1) and (2) occurs, and the performance on ice is greatly improved.

The average particle size of the eggshell powder (1) is 20 μm or less, preferably 10 μm or less. If the average particle diameter of the eggshell powder (1) exceeds 20 μm, the resulting pores become large and the wrinkle portion decreases, so that a sufficient scratching effect cannot be obtained. Moreover, the average particle diameter of eggshell powder (1) is preferably 3 μm or more, and more preferably 5 μm or more. If the average particle diameter of the eggshell powder (1) is less than 3 μm, the resulting unevenness tends to be flat and performance on ice tends not to be expected. In addition, the average particle diameter of eggshell powder (1) is measured using a particle size distribution measuring device.

30 mass% or more is preferable and, as for the content rate of eggshell powder (1) with respect to the total content of eggshell powder (1) and (2), 40 mass% or more is more preferable. When the content is less than 30% by mass, the number of small pores decreases, and a sufficient edge effect tends not to be obtained. Moreover, 70 mass% or less is preferable and, as for the content rate of eggshell powder (1), 60 mass% or less is more preferable. When the content exceeds 70% by mass, large pores tend to be reduced and a sufficient water absorption effect tends not to be obtained.

The average particle diameter of the eggshell powder (2) is 40 μm or more, preferably 45 μm or more, more preferably 50 μm or more. If the average particle diameter of the eggshell powder (2) is less than 40 μm, there will be no sufficiently large pores and a sufficient water absorption effect will not be obtained. Moreover, the average particle diameter of eggshell powder (2) is 200 μm or less, preferably 150 μm or less, more preferably 100 μm or less, and further preferably 80 μm or less. If the average particle diameter of the eggshell powder (2) exceeds 200 μm, the wear resistance will be reduced, or the contact area between the rubber and the icy and snowy road surface will be extremely reduced due to irregularities exceeding a certain level, and conversely on ice. There is a tendency to reduce performance. In addition, the average particle diameter of eggshell powder (2) is measured using a particle size distribution measuring device.

The content of the eggshell powder is 5 parts by mass or more, preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. When the content of eggshell powder is less than 5 parts by mass, the performance on ice is not improved. The content of eggshell powder is 25 parts by mass or less, preferably 20 parts by mass or less, with respect to 100 parts by mass of the rubber component. When the content of the eggshell powder exceeds 25 parts by mass, the dispersion becomes worse when kneaded into rubber, and the wear resistance is lowered. The content of chicken eggshell powder means the sum of the contents of eggshell powder (1) and (2).

The rubber composition used in the present invention has a Mooney viscosity at 130 ° C. of preferably 75 or less, more preferably 70 or less, and even more preferably 65 or less, before curing.

The hardness of the cured product of the rubber composition is preferably 58 degrees or more, more preferably 60 degrees or more, further preferably 62 degrees or more, and most preferably 64 degrees or more in terms of JIS-A hardness. By setting the hardness to 58 degrees or more, good block rigidity can be secured, and steering stability, good uneven wear resistance, and wear resistance can be secured. On the other hand, the hardness is preferably 75 degrees or less, more preferably 70 degrees or less, and still more preferably 67 degrees or less. By setting the hardness to 75 degrees or less, excellent performance on ice and snow can be achieved.

The tan δ of the crosslinked product obtained by crosslinking the rubber composition is preferably tan δ measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2% and a frequency of 10 Hz, of 0.17 or less. Or less, more preferably 0.13 or less.

The studless tire for trucks / buses or light trucks of the present invention has a tire tread produced from the rubber composition. Here, light trucks are SUVs, vans (large conventional vans and minivans), pickup trucks, and the like.

The studless tire is manufactured by a usual method using the rubber composition. That is, it can be produced by preparing a tire tread using the rubber composition appropriately blended with the compounding agent as necessary, bonding together with other members, and heating and pressing on a tire molding machine.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
Natural rubber (NR): RSS # 3
BR1: BR150B manufactured by Ube Industries, Ltd. (cis 1,4 bond amount 97%, ML _{1 + 4} (100 ° C.) 40, toluene solution viscosity at 25 ° C. 48 cps, Mw / Mn 3.3)
BR2: BR360L manufactured by Ube Industries, Ltd. (cis 1,4 bond amount 98%, ML _{1 + 4} (100 ° C.) 51, toluene solution viscosity at 25 ° C. 124 cps, Mw / Mn 2.4)
BR3: BR A manufactured by Ube Industries, Ltd. (prototype, cis 1,4 bond 98%, ML _{1 + 4} (100 ° C.) 47, toluene solution viscosity at 25 ° C. 122 cps, Mw / Mn 3.3)
Carbon Black: Dia Black A (N110 (SAF) carbon, average particle diameter 19 nm, DBP oil absorption 116 ml / 100 g, nitrogen adsorption specific surface area 142 m ² / g) manufactured by Mitsubishi Chemical Corporation
Silica: Ultrasil VN3 manufactured by Degussa (N ² SA: 175 m ² / g)
Eggshell powder 1: egg calcium (calhope) manufactured by Kewpie Co., Ltd. (average particle size 10 μm)
Eggshell powder 2: egg calcium (calhope) manufactured by Kewpie Co., Ltd. (average particle size 50 μm)
Stearic acid: Anti-paulownia reversion inhibitor manufactured by NOF Corporation: Activator 73A manufactured by Straktor ((i) Aliphatic carboxylic acid zinc salt: fatty acid derived from palm oil (carbon number: 8-12) Zinc salt, (ii) aromatic carboxylic acid zinc salt: zinc benzoate, content molar ratio: 1/1, zinc content: 17% by mass)
Zinc oxide: Zinc oxide type 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N'-phenyl-p- manufactured by Ouchi Shinsei Chemical Co., Ltd.) Phenylenediamine)
Wax: Ozoace wax manufactured by Nippon Seiwa Co., Ltd. Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2 manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) -Benzothiazolylsulfenamide)

Examples 1-9 and Comparative Examples 1-6
In accordance with the formulation shown in Table 1, using a Banbury mixer, the amount of chemicals shown in Step 1 of Table 1 other than sulfur and vulcanization accelerator is added, and the discharge temperature is about 150 ° C. for 5 minutes. Kneaded. Then, sulfur and a vulcanization accelerator in the blending amounts shown in Step 2 are added to the mixture obtained in Step 1, and the mixture is kneaded at about 80 ° C. for 3 minutes using an open roll. I got a thing. The obtained unvulcanized rubber composition was molded into a tread shape, bonded to another tire member, and vulcanized for 35 minutes under the conditions of 150 ° C. and 25 kgf. A studless tire (tire size: 11R22.5) was produced.

Each sample was evaluated by the method described below.

(Reversion property)
Using a curast meter, the vulcanization curve of the unvulcanized rubber composition at 160 ° C. was measured. The maximum torque increase value (MH-ML) value is set to 100, the torque increase value 20 minutes after the start of vulcanization (M (20 minutes) -ML) is shown as a relative value, and the relative value is subtracted from 100. Reversion rate. The smaller the reversion rate, the better the reversion is suppressed and better.

(hardness)
According to JIS K6253 “Method for testing hardness of vulcanized rubber and thermoplastic rubber”, the hardness of the vulcanized rubber specimen of each example was measured with a type A durometer.

(Performance on ice and snow)
Using the studless tire of each example, actual vehicle performance was evaluated on ice and snow under the following conditions. As winter pneumatic tires, 11R22.5 studless tires for trucks and buses were manufactured, and these tires were mounted on 4-ton vehicles. The test place was the Hokkaido Asahikawa test course of Sumitomo Rubber Industries, Ltd., the temperature on ice was -1 to -6 ° C, and the temperature on snow was -2 to -10 ° C.
-Braking performance (on-ice braking stop distance): The stop distance on ice required to depress and stop the lock brake at 30 km / h was measured. And it computed from the following formula by making Comparative Example 1 into a reference.
(Braking performance index) = (braking stop distance of comparative example 1) ÷ (stop distance) × 100
・ Handling performance: Using the same vehicle, we measured the start, acceleration, and stop, and evaluated by feeling. Feeling evaluation is based on Comparative Example 1 as 100, with the test driver clearly judging that the performance has improved, 120, and a good level that has never been seen so far as 140. Scoring was performed.

(Abrasion resistance)
A test piece having a thickness of 5 mm was cut out from the tread of the studless tire for trucks and buses of each example, and using a Lambone abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd., surface rotation speed 50 m / min, additional load 3.0 kg, The amount of wear was measured under the condition of a sandfall rate of 15 g / min and a slip rate of 20%, and the reciprocal of the amount of wear was taken. The reciprocal of the amount of wear in Comparative Example 1 was taken as 100, and the other reciprocal of the amount of wear was expressed as an index. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.

(Rolling resistance)
Samples were cut from the treads of the truck and bus studless tires of each example, and using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd., the temperature was 70 ° C., the initial strain was 10%, the dynamic strain was 2%, and the frequency was 10 Hz. Under the conditions, loss tangent (tan δ) was measured.

(Bloom)
After vulcanization, visually check the bloom state, x is clearly precipitated, △ is confirmed by magnifying glass, △, no bloom is seen immediately after vulcanization, The case where no bloom was observed even after 3 weeks from vulcanization was marked with ◎.

(Viscosity / workability)
Viscosity is determined by preheating for 1 minute using a Mooney viscosity tester according to JIS K 6300-1 “Unvulcanized rubber—Physical properties—Part 1: Determination of viscosity and scorch time using Mooney viscometer”. Under the heated temperature condition of 130 ° C., the small rotor was rotated, and the Mooney viscosity (ML ^{1 +} 4/130 ° C.) of the unvulcanized rubber composition after 4 minutes was measured. The numbers after the decimal point are rounded off.

On the basis of Mooney viscosity, the processability was evaluated as x for 76 or more, Δ for 71 or more and 75 or less, ◯ for 66 or more and 70 or less, and ◎ for 65 or less.

(Adhesion test)
Adhesive strength of an unvulcanized rubber composition at a temperature of 23 ° C. and a humidity of 55% under conditions of a rising speed of 30 mm / min and a measurement time of 2.5 seconds using a PICMA / tack tester manufactured by Toyo Seiki Seisakusho Co., Ltd. [N] was measured. Further, the tackiness index of Comparative Example 1 was set to 100, and the tackiness was expressed as an index by the following formula. The larger the tackiness index, the greater the tackiness, and the better the tackiness.
(Adhesive index) = (Adhesive strength of each formulation / Adhesive strength of Comparative Example 1) × 100

Table 1 shows the evaluation results of the above tests.

In all the samples of the examples, the reversion rate is low, the hardness is appropriate, and both high handling performance, braking performance on ice, and wear resistance performance are compatible. In Examples 3 to 9, in which the BR ratio is particularly high, all of them have a low reversion rate, achieve particularly high handling performance and braking performance on ice, and prevent a decrease in wear resistance even though the BR ratio is high. Yes.

Further, in Examples 6 and 8, BR having a cis content of 95% or more and a toluene solution viscosity at 25 ° C. of 80 to 200 cps, more preferably 110 to 150 cps and Mw / Mn of 3.0 or less, in Examples 7 and 9, , Mw / Mn 3.0 to 3.4 is blended to improve wear resistance. In particular, by improving the workability, the dispersion state of the silica is improved, and the wear resistance in the formulation having a large amount of silica is also improved. Further, the mixture of the aliphatic carboxylic acid zinc salt and the aromatic carboxylic acid zinc salt not only improves the reversion, but also improves the processability.

In Comparative Examples 1 and 3 to 5 in which eggshell powder was blended and a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid was not contained, the wear resistance was lowered. In addition, the hardness was low, and the handling performance and uneven wear resistance also decreased. Furthermore, the workability was very poor. In Comparative Example 6 containing a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid and stearic acid, the tackiness was inferior to that of the example.

Claims (2)

It contains a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, contains 35% by mass or more of butadiene rubber in 100% by mass of the rubber component , and the content of stearic acid with respect to 100 parts by mass of the rubber component A studless tire for trucks / buses or light trucks using a rubber composition of 0.05 parts by mass or less as a tread. The studless tire for trucks / buses or light trucks according to claim 1, wherein the rubber composition further contains 5 parts by mass or more of silica with respect to 100 parts by mass of the rubber component.